Nonintrusive measurements of the boundary layer developing on a single and two circular cylinders

 The boundary layers developing on a single and two tandem circular cylinders were examined using multiple hot-film sensor arrays for Re=2.4–5.1×10⁴. Hot-wire and surface pressure measurements, and smoke-wire flow visualization were also made to better understand the flow pattern and the evolution of the vortex street. The results show that, by use of the sensor arrays in conjunction with a bank of constant-temperature anemometers, (i) the effects of the upstream cylinder on the boundary layer developing on the downstream cylinder, (ii) the frequency of the vortex shedding, and (iii) the locations of flow separation and reattachment can be determined non-intrusively and simultaneously. These measurement capabilities will provide a practical means for the characterization and manipulation of unsteady flow phenomena. Received: 27 October 1996 / Accepted: 13 February 1997